Figure REF  demonstrates several pressure isotherms \(\tilde{p}=\tilde{p}(\tilde{n})\)  at \(\tilde{T}\le 1\) .
These isotherms include the metastable and unstable parts denoted in Fig. REF  (a) by dashed and dotted lines, respectively. A region of the unstable isotherms with \(\partial \tilde{p}(\tilde{n},\tilde{T})/\partial \tilde{n} <0 \)  shown with grey colour in Fig. REF  is restricted by the left and right spinodals where \(\partial \tilde{p}(\tilde{n},T)/\partial \tilde{n} = 0 \) .
In the \((\tilde{n},\tilde{T})\) -regions with \(\partial \tilde{p}(\tilde{n},\tilde{T})/\partial \tilde{n} <0\)  the system can not exist
in the homogeneous state. Instead, it behaves as an inhomogeneous mixture of the gas and liquid with particle number densities \(n_{\rm g}\)  and \(n_{\rm l}\) , respectively. According to the Gibbs criteria these two phases should have the same temperatures, chemical potentials, and pressures. A region occupied by the liquid-gas mixed phase is restricted by the left (gaseous) and right (liquid) binodals with particle number densities \(n_{\rm g}\)  and \(n_{\rm l}\) , respectively. These binodals are shown by the blue solid lines in Fig. REF  (b). The pressure isotherms inside the mixed phase shown by the horizontal solid lines in Fig. REF  (a) are obtained from the Gibbs conditions or, equivalently, with the Maxwell construction of equal areas [1]}.
